Comparação da adição de nanotubos de carbono funcionalizados e não funcionalizados nas propriedades de concretos submetidos a temperaturas elevadas

Abstract

Carbon nanotubes (CNTs) have excellent mechanical properties. When applied to concrete, they function as reinforcement, improving the microstructure of the matrix and preventing the propagation of cracks. However, there are still research gaps involving the behavior of CNTs at high temperatures, an important topic in order to guarantee human safety and the preservation of buildings in the event of fire. Within this context, the objective of this research is to evaluate the thermomechanical behavior of a concrete with the addition of functionalized and nonfunctionalized CNTs. For this purpose, three types of concrete were tested: conventional (REF), with functionalized CNTs (NTC FUN) and with non-functionalized CNTs (NTC NF); both at a content of 0.15% in relation to the cement mass. Scanning electron microscopy (SEM), specific mass, absorption, void index, determination of ultrasonic wave propagation speed (VPU), compressive and tensile strength were carried out. The concretes were tested at room temperature and after heating to 300°C, 600°C and 900°C in a muffle furnace. The SEM results showed the poor dispersion of CNTs and lack of homogeneity in the nanomaterial in the concrete. No significant differences were identified between the dispersion of the two types of CNTs. There is no difference in the specific mass, void ratio and VPU results for the NTC FUN and NTC NF traces at all temperatures studied. There is no difference between the mass loss at 300°C and 600°C of the traces with the addition of CNTs. At a temperature of 900°C, the mass loss of the NTC NF mix was greater than that of the NTC FUN mix. There is no difference between the water absorption of traces with the addition of CNTs at room temperatures, 300°C and 600°C. At 900°C, the absorption of the NTC NF trace was higher than the NTC FUN trace. At room temperature, the compressive strength results of the traces with the addition of CNTs were similar. Regarding residual compressive strength, the NTC FUN mix showed better performance at a temperature of 300°C, possibly due to the strong bond between the functional groups of the CNTs functionalized with the cementitious matrix. At room temperature and after exposure to high temperatures there was no difference in the tensile strength of the NTC FUN and NTC NF traces. It can be concluded that the addition of functionalized CNTs improves the mechanical behavior of concrete at the beginning of exposure to high temperatures in fire situations, but further work is recommended to understand the phenomena behind the dispersion of this material.